On the mechanisms of charge weld evolution in aluminum extrusion

Abstract

This study aims to provide new insights into the governing mechanisms of material property evolution within the charge weld zone in the hot extrusion process of aluminum profiles. A set of 6xxx series aluminum alloy tubular profiles was produced through carefully designed industrial experiments of billet-to-billet extrusion. The evolution of material integrity within the charge weld zones was experimentally characterized by microhardness tests, optical microscopy, scanning electron microscopy (SEM), and drift-expansion tests. The experimental analyses reveal that the material integrity of charge welds gradually increases from the onset to the end, primarily driven by the ‘local’ pressure history experienced. Towards the end of the charge weld zone, grooves and holes, and oxide particles gradually vanish, leading to enhanced material integrity. A through-process finite element (FE) model was developed using QForm-Extrusion software to analyze the thermo-mechanical history of charge weld formation, providing a deeper understanding of how material properties evolve and the underlying mechanisms governing this evolution. The model was experimentally validated in terms of the extrusion load and distribution of the charge welds in extruded profiles. Overall, the new insights gained in this study offer valuable knowledge for enhancing the process and quality control in billet-to-billet extrusion, as well as reducing in-process scrap towards more sustainable production of aluminum profiles.